Joint for folding rules



Patented Nov. 3, 1931 UNITED STATES PATENT OFFICE I EUGENE J. WITCHGERfOF SAGINAW, MICHIGAN, ASSIGNOR TO LUFKIN RULE 00., OF

SAGINAW, MICHIGAN, A CORPORATION OF MICHIGAN JOINT FOR FOLDING RULES Application filed December 9, 1929. Serial No. 412,603.

This invention relates to means for accurately maintaining the length of a zigzag folding rule. It comprises a novel latch device that prevents the overlapping ends of the sections from shifting endwise one upon the other even though the pivots of the several sections become worn and develop an appreciable amount of play that ordinarily would render the rule inaccurate. For instance, an eight foot rule with seven joints of ordinary construction may show as much as one-eighth inch total variation in length, evidenced by elongation when the rule is stretched, and by shortening when it is compressed endwise.

This invention is especially applicable to zigzag rule oints of the kind that comprises two plates pivoted together and springpressed toward each other, the plates being embossed in such a way as to nest one with the other, lifting apart when the rule sections are crosswise, and snapping into faceto-face contact when extended.

The object of the invention herein claimed is to provide in conjunction with the hinge, a novel latch structure that permanently maintains the accuracy of the original length of the rule by holding the plates against all endwise movement one upon the other; in fact, endwise movement however slight is not even permitted to start.

The improved lock device in no way interferes with the normal'working of a zigzag rule. Its hinge-like folding and unfolding, the snapping into alinement, and the separating of the plates preparatory to extending or folding the sections are all performed exactly as heretofore.

The lock is always out of action except when the two plates are either in face-to-face contact, or are nearly so, that is, when the embossed parts of the plates are either completely nested or else are so nearly nested that the two embossments are in the act of engaging with each other.

Another object of the invention is to provide the co-acting' hinge plates with an auxiliary device for leading the end-locking members into mutual engagement.

With the foregoing and certain other objects in view, which will appear later in the specification, the invention comprises the devices described and claimed and the equivalents thereof.

In the drawings Fig. 1 is a longitudinal sectional view of a rule joint with my improvement applied thereto.

Fig. 1a is a fragmentary sectional detail of the locking projection shown in Fig. 1.

Fig. 2 is a plan View, partly broken away, showing the hinged plates locked together.

Fig. 3 is a plan and end view respectively of the slotted hinge plate.

Fig. at is a plan'and end view respectively of the co operating hinge plate with locking and centering projections.

Fig. 5 is a plan view of a rule joint assembled, showing the relation between the slots and projections just prior to being brought together and locked.

As is clearly shown in the drawings, a zigzag rule of the kind to which my improvement is applicable is composed of sections 1 having graduation lines 2. The sections are hinged together by means of a known joint structure consisting of the hinge plates 3, 4. one being embossed to provide a depressed part 3a, the other having a complemental raised portion 4a. Pivot 5 pierces the two plates. A spring 6 presses the plates together, but yields to let them move apart under the cam-like action of the raised portion 4a whenever the rule sections are given a hinge movement about the pivot, it being understood that the embossed portions 3a, 4a of the plates have sloping marginal walls 3?), 4b, enabling the spring to bring them into nested position and alinement with a final snap action.

According to my invention one of the usual plates, 4, is provided on its face with a projection 7 having abrupt end walls 7a, 76. A co-operating transverse slot 8 is formed in the opposing plate 3. The slot is preferably curved, with pivot 5 as center. Slot 8 is made slightly wider at its ends 8a, 85 than in its middle, to insure the entrance of projection 7 into the slot near one end, notwithstanding any looseness around the pivot. Toward its middle the slot narrows and the abrupt end walls 7a, 7b of projection 7 fit closely therein in locked engagement. However, for the sake of clearness in the drawings a clearance is shown at the walls 7a, 76. These walls are the working faces of projection 7 and constitute stops that block all tendency of the, plates to shift in the direction of the length of the rule when it is pushed or pulled endwise. The locking projection 7 can not play, nor can it SllP, mount or climb out of the slot. The height of projection 7 above the face of its plate 4 is less than the distance between the two plates 3, 4 when separated, hence late 3 can pass freely over the projection while the rule is bein folded or extended. Slot 8 may be a recess if desired.

The accurate entry of projection 7 into elongated slot 8 is further assured by a device that will now be described.

A projection 9 and a complemental aperture 10 are formed in the respective plates 4, 3, preferably at a place remote from projection 7. The working faces 9a, 9b of projection 9 are tapered. Aperture 10 is elongated and widened at its ends the same as slot 8. When plates 3, 4 are snapped together by spring 6 the relatively tapered tip of projection 9 enters aperture 10 near an en thereof and acts as a somewhat pointed pin to guide projection 7 and slot 8 into register so the graduation lines 2 common to the two overlapping rule sections will exactly match.

If pivot gets so loose that locking projection 7 fails to enter slot 8 properly, but instead rides on the edge, then aperture and tapered projection 9 come into play and put 7 and 8 into register by properly centering them.

Although the primary or locking projection 7 is herein shown and described as being a single boss with two abrupt faces 7a, 7?) that abut against the edges of slot 8, it is obviously not essential to the operativeness of my device that both faces be on the same projection. As a matter of fact they may be on separate projections situated in difierent locations on the plates without departing from my invention, so long as they together make a lock that blocks endwise movement of the rule sections one upon the other, such eouivalent arrangements being within the scope of the invention as herein claimed.

By the means described I have provided a simple, eifective device for interlocking the plates so as to prevent all relative endwise n'ioveinent when the rule is extended. Accuracy is maintained notwithstanding wear at the pivot and irrespective of the condition of the spring. The lock relieves the pivot of all endwise stress and makes the rule more tight. In that respect my invention differs from prior devices. aimed at the same result, but which fell short of its accomplishment berauae they were so arranged that the effectiveness of the locking function depended upon the strength of the spring.

An exam le of such earlier devices is found in Patent 0. 928,174 issued July 13, 19 O9, that shows and describes a joint comprising two metallic plates embossed for nesting, and depending upon the embossment for a locking function. An endwise pull on the rule when extended would cause the spring at each joint to yield, allowing the embossed and nested parts of the plates to climb and slip, altering the length of the rule and impairing its accuracy.

Zigzag rules are commonly made with wood or metal sections and the spring shown and described in the foregoing disclosure is employed, but sometimes such sections are employed wherein the embossed plates are used ut the spring is dispensed with, the resilient material of the overlapping sections being relied upon to provide the required spring action, all in known manner. It will be understood that this invention is applicable to folding rules made of metal, as well as wood.

Having thus described my invention, what I claim and desire to secure by Letters Patent 1s:

1. In combination, a rule joint comprising d plates pivoted together in yieldingly interlocking relation, an abrupt-walled projection on one plate, a complemental recess wider at its ends than at its middle, formed in the opposite plate, contiguous faces of said projection and recess adapted to engage each other in close endwise relation and constituting means, independent of the pivotal connection, for holding said plates against longitudinal shifting one upon the other.

2. In combination with a structure as set forth in claim 1, a tapered projection formed on one of said plates, and a complemental aperture in the opposite plate, together constituting a centering device for guiding said abrugt-walled projection into its recess.

n combination. a rule joint comprising plates pivoted together in yieldingly interlocking relation, an abrupt-walled projection on one plate, a complemental transverse slot in the opposite plate, said slot being wider at its ends than in the middle, said projection 5. In combination, a rule joint comprising plates pivoted together in yieldingly interlocking relation, an abrupt-walled projection on one plate, a complemental elongated recess in the opposite plate, the edges of said 'recess presenting laterally convergent guiding margins, said projection and the convergent margins of sald recess constitutin co-acting means, independent of the pivota connection, for holding said plates against longitudinal shifting one upon the other.

6. Measuring rule sections having overlapping endssecured together by a huge joint comprising a pair of plates, a spring yieldingly pressing said plates together, a rivet pivotally joining said plates and spring, the contiguous faces of said plates embowed to foam complemental recesses and projections an holdlng the plates in alinement when nested, latching means comprising complemental projections and recesses integral with said.

plates, said latching means being inde endprojection on a plate member 0 ent of said pivotal connection, and 0 said embossed recesses, and arranged for releasably fastening said plates together in a manner rendering them, when nested, immovable lengthwise one upon the other irrespective of worn conditions of the pivotal joint or of the plates, and uiding means \on said plates arran ed to msure the engagement of said late ing means.

7. In combination with a foldin rule com- I posedof sections connected for ahnement by plates pivoted together, a locking device operativel independent of the 'oint alining mechamsm' and characterized b havin a said joint, the other plate member formed with a recess positioned transversely thereof, end walls of saidprojection sha dvto'fit complemental edges of the recess in close lockin relation when said rule is extended where y initial accurac in length is maintained independently o wear at the ivot of said joint, and

means associated with said plates for brin ing said locking device into operative position when the rule is extended.

In testimony whereof I aflix my si ature EUGENE J. WITCH ER.

ositioned lengthwise of the plates for 

